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Lecture 10 Reliability

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Published on June 26, 2007

Author: Funtoon

Source: authorstream.com

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ReliabilityOctober 26, 2004:  Reliability October 26, 2004 Today:  Today DFDC (Design for a Developing Country) HW November 2 detailed design Parts list Trade-off Midterm November 4 Factory Visit November 16th Midterm:  Midterm Presentation Purpose- a midcourse correction less than 15 minutes with 5 minutes discussion Approx. 7 power point slides- all should participate in presentation Show what you have done Show what you are going to do Discuss issues, barriers and plans for overcoming (procedural, team, subject matter, etc. Scored on originality, candor, thoughtfullness, etc. not on total amount accomplished Schedule today from 1:00 to 4:00 (speaker at 4:00 PM) Reliability The probability that no (system) failure will occur in a given time intervalA reliable system is one that meets the specifications Do you accept this?:  Reliability The probability that no (system) failure will occur in a given time interval A reliable system is one that meets the specifications Do you accept this? What do Reliability Engineers Do?:  What do Reliability Engineers Do? Implement Reliability Engineering Programs across all functions Engineering Research manufacturing Testing Packaging field service Reliability as a Process module:  Reliability as a Process module Reliability Goals Schedule time Budget Dollars Test Units Design Data Reliability Assurance Module Internal Methods Design Rules Components Testing Subsystem Testing Architectural Strategy Life Testing Prototype testing Field Testing Reliability Predictions (models) INPUT Product Assurance Early product failure:  Early product failure Strongest effect on customer satisfaction A field day for competitors The most expensive to repair Why? Rings through the entire production system High volume Long C/T (cycle time) Examples from GE (but problem not confined to GE!) GE Variable Power module for House Air Conditioning GE Refrigerators GE Cellular Early Product Failure:  Early Product Failure Can be catastrophic for human life Challenger, Columbia Titanic DC 10 Auto design Aircraft Engine Military equipment Reliability as a function of System ComplexityWhy computers made of tubes (or discrete transistors) cannot be made to work:  Reliability as a function of System Complexity Why computers made of tubes (or discrete transistors) cannot be made to work Three Classifications of Reliability Failure:  Three Classifications of Reliability Failure Type Early (infant mortality) Wearout (physical degradation) Chance (overstress) Old Remedy- Repair mentality Burn-in Maintenance In service testing Bathtub Curve:  Bathtub Curve Infant Mortality Useful life No memory No improvement No wear-out Random causes Wear out Failure Rate #/million hours Time Reliability:  Reliability Age Prob of dying in the next year (deaths/ 1000) From the Statistical Bulletin 79, no 1, Jan-Mar 1998 Early failure causes or infant mortality (Occur at the beginning of life and then disappear):  Early failure causes or infant mortality (Occur at the beginning of life and then disappear) Manufacturing Escapes workmanship/handling process control materials contamination Improper installation Chance Failures (Occur throughout the life a product at a constant rate):  Chance Failures (Occur throughout the life a product at a constant rate) Insufficient safety factors in design Higher than expected random loads Human errors Misapplication Developing world concerns Wear-out(Occur late in life and increase with age):  Wear-out (Occur late in life and increase with age) Aging degradation in strength Materials Fatigue Creep Corrosion Poor maintenance Developing World Concerns Failure Types:  Failure Types Catastrophic Degradation Drift Intermittent Failure Effects(What customer experiences):  Failure Effects (What customer experiences) Noise Erratic operation Inoperability Instability Intermittent operation Impaired Control Impaired operation Roughness Excessive effort requirements Unpleasant or unusual odor Poor appearance Failure Modes:  Failure Modes Cracking Deformation Wear Corrosion Loosening Leaking Sticking Electrical shorts Electrical opens Oxidation Vibration Fracturing Reliability Remedies:  Reliability Remedies Early Wearout Chance Quality manufacture/Robust Design Physically-based models, preventative maintenance, Robust design (FMEA) Tight customer linkages, testing, HAST Reliabilitysemi-empirical formulae:  Reliability semi-empirical formulae Wear out Chance Failure Early failure k =constant failure rate m=MTBF =pdf Failures Vs time as a function of Stress:  Failures Vs time as a function of Stress High Stress Medium Stress Low Stress Highly Accelerated Stress Testing:  Highly Accelerated Stress Testing Test to Failure Fix Failed component Continue to Test Appropriate for developing world? Duane Plot Reinertson p 237:  Duane Plot Reinertson p 237 Log Failures per 100 hours Log Cumulative Operating Hours x x x x x x x x x x x x x x x Actual Reliability Required Reliability at Introduction Predicted Integration into the Product Development Process FMEA- Failure Modes and Effects Analysis:  Integration into the Product Development Process FMEA- Failure Modes and Effects Analysis Customer Requirements Baseline data from Previous Products Brainstorm potential failures Summarize results (FMEA) Update FMEA Baseline data from Previous Products Feed results to Risk Assessment Process Use at Design Reviews Develop Failure Compensation Provisions Test Activity Uncovers new Failure modes Failure prob- through test/field data Probabilities developed through analysis Risk Assessment process:  Risk Assessment process Assess risk Program Risk Market Risk Technology Risk Reliability Risk Systems Integration Risk Devise mitigation Strategy Re-assess Fault Tree analysis:  Fault Tree analysis Seal Regulator Valve Fails Valve Fails Open when commanded closed Fails to meet response time Excessive leakage Regulates High Regulates Low Fails closed when commanded open Excessive hysteresis or or or Excessive port leakage Excessive case leakage Fails to meet response time Fails to meet response time 1 5 4 3 2 6 7 8 9 Next Page Fault Tree analysis (cont):  Fault Tree analysis (cont) Valve Fails Open when commanded closed 1 Valve Fails Open when commanded closed or Mechanical Failure Selenoid Electrical Failure of Selenoid or or Open Circuit or Coil short Insulation Solder Joint Failure Wire Broken seals Material selection wear Material selection Transient electro mechanical force FMEA:  FMEA FMEA Root Cause Analysis:  FMEA Root Cause Analysis Fault Tree Analysis- example:  Fault Tree Analysis- example Example: A solar cell driven LED Reliability Management:  Reliability Management Redundancy Examples Computers memory chips? Aircraft What are the problems with this approach 1. Design inelegance expensive heavy slow complex 2. Sub optimization Can take the eye off the ball of improving component and system reliability by reducing defects Where should the redundancy be allocated system subsystem board chip device software module operation Other “best practices”:  Other 'best practices' Fewer Components Small Batch Size (why) Better material selection Parallel Testing Starting Earlier Module to systems test allocation Predictive (Duane) testing Look for past experience emphasize re-use over-design e.g. power modules Best: Understand the physics of the failure and model e.g. Crack propagation in airframes or nuclear reactors Other suggestions?:  Other suggestions?

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